Download How Cells Harvest Chemical Energy

Chapter 6
How Cells Harvest Chemical
Energy
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
How Is a Marathoner Different from a Sprinter?
• Human muscles contain two different types of
muscle fibers
–
That perform differently under different
conditions
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The different types of muscle fibers
– Function either aerobically, with oxygen,
or anaerobically, without oxygen
• Cellular respiration
– Is the process by which cells produce
energy aerobically
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
1
INTRODUCTION TO CELLULAR RESPIRATION
6.1 Photosynthesis and cellular respiration provide
energy for life
• Cellular respiration makes ATP and consumes O2
– During the oxidation of glucose to CO2 and
H2O
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Photosynthesis uses solar energy
–
To produce glucose and O2 from CO2 and H2O
Sunlight energy
ECOSYSTEM
Photosynthesis in
chloroplasts
Glucose
CO2
+
+
H2 O
O2
Cellular respiration in
mitochondria
ATP
(for cellular work)
Heat energy
Figure 6.1
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6.2 Breathing supplies oxygen to our cells and
removes carbon dioxide
• Breathing provides for the exchange of O2 and CO2
–
Between an organism and its environment
O2
CO2
Breathing
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose + O2
Figure 6.2
CO2 + H2O + ATP
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6.3 Cellular respiration banks energy in ATP
molecules
• Cellular respiration breaks down glucose
molecules
– And banks their energy in ATP
C6H 12O6
Glucose
+
6
O2
Oxygen gas
6
CO2
+
Carbon
dioxide
6
H2O
+
Water
ATPs
Energy
Figure 6.3
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CONNECTION
6.4 The human body uses energy from ATP for
all its activities
• ATP powers almost all cellular and body activities
Table 6.4
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6.5 Cells tap energy from electrons “falling” from
organic fuels to oxygen
• Electrons lose potential energy
– During their transfer from organic
compounds to oxygen
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• When glucose is converted to carbon dioxide
– It loses hydrogen atoms, which are
added to oxygen, producing water
Loss of hydrogen atoms
(oxidation)
C6H 12O6 + 6 O2
6 CO2
+
6 H2O + Energy
Glucose
(ATP)
Gain of hydrogen atoms
(reduction)
Figure 6.5A
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• Dehydrogenase removes electrons (in
hydrogen atoms) from fuel molecules
(oxidation)
– And transfers them to NAD+ (reduction)
H
O
NAD+
Oxidation
H
+
O + 2H
Dehydrogenase
Reduction
2H
2H+ +
NADH
+
H+
(carries
2 electrons)
2e−
Figure 6.5B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• NADH passes electrons
–
To an electron transport chain
• As electrons “fall” from carrier to carrier and finally to O2
–
Energy is released in small quantities
NADH
!ATP
NAD+
+
2e−
Controlled
release of
energy for
synthesis
of ATP
H+
tra Ele
ns c
po t r o
rt n
ch
ain
2e−
2 H+
Figure 6.5C
1
2
O2
H2O
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4
STAGES OF CELLULAR RESPIRATION AND
FERMENTATION
• 6.6 Overview: Cellular respiration occurs in
three main stages
• Cellular respiration
– Occurs in three main stages
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• Stage 1: Glycolysis
– Occurs in the cytoplasm
– Breaks down glucose into pyruvate,
producing a small amount of ATP
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• Stage 2: The citric acid cycle
– Takes place in the mitochondria
– Completes the breakdown of glucose,
producing a small amount of ATP
– Supplies the third stage of cellular
respiration with electrons
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5
• Stage 3: Oxidative phosphorylation
– Occurs in the mitochondria
– Uses the energy released by “falling”
electrons to pump H+ across a
membrane
– Harnesses the energy of the H+ gradient
through chemiosmosis, producing ATP
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• An overview of cellular respiration
NADH
High-energy
electrons
carried by NADH
NADH
FADH2
and
GLYCOLYSIS
Glucose
Pyruvate
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC ACID
CYCLE
Mitochondrion
Cytoplasm
CO2
ATP
ATP
Substrate-level
phosphorylation
ATP
CO2
Substrate-level
phosphorylation
Oxidative
phosphorylation
Figure 6.6
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6.7 Glycolysis harvests chemical energy by oxidizing
glucose to pyruvate
• In glycolysis, ATP is used to prime a glucose
molecule
–
Which is split into two molecules of pyruvate
2
NAD+
2
NADH
+ 2
H+
Glucose
2 Pyruvate
2 ADP
+2
P
2
ATP
Figure 6.7A
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6
• Glycolysis produces ATP by substrate-level
phosphorylation
–
In which a phosphate group is transferred
from an organic molecule to ADP
Enzyme
P
Adenosine
P
P
ATP
ADP
P
Organic molecule
(substrate)
P
Figure 6.7B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• In the first phase of glycolysis
– ATP is used to energize a glucose
molecule, which is then split in two
Steps 1 – 3 A fuel molecule is energized,
using ATP.
PREPARATORY PHASE
(energy investment)
Glucose
ATP
Step
1
ADP
P
Glucose-6-phosphate
P
Fructose-6-phosphate
P
Fructose-1,6-diphosphate
2
ATP
3
ADP
P
Step 4 A six-carbon intermediate splits
into two three-carbon intermediates.
4
Figure 6.7C
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• In the second phase of glycolysis
– ATP, NADH, and pyruvate are formed
P
Step
6
9
NADH.
P
Glyceraldehyde-3-phosphate
(G3P)
5 A redox reaction generates
NAD+
+H+
P
ADP
P
6
7
6
ATP
P
P
7
P
8
8
H2 O
7
P 3 -Phosphoglycerate
7
8
2-Phosphoglycerate
8
H2 O
P
P
9
ADP
Phosphoenolpyruvate
(PEP) 9
ADP
9
Figure 6.7C
6
P 1,3 -Diphosphoglycerate
ADP
ATP
ATP
ENERGY PAYOFF PHASE
5
P 6 NADH
+H+
P
P
NADH
Steps 6 – 9 ATP and pyruvate
are produced.
NAD+
5
9
ATP
Pyruvate
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6.8 Pyruvate is chemically groomed for the citric acid
cycle
• Prior to the citric acid cycle
–
Enzymes process pyruvate, releasing CO2
and producing NADH and acetyl CoA
+ H+
NADH
NAD+
2
CoA
Pyruvate
Acetyl CoA
(acetyl coenzyme A)
1
3
CO2
Coenzyme A
Figure 6.8
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6.9 The citric acid cycle completes the oxidation of organic
fuel, generating many NADH and FADH2 molecules
• In the citric acid cycle
–
The two-carbon acetyl part of acetyl CoA is
oxidized
Acetyl CoA
CoA
CoA
CITRIC ACID CYCLE
2 CO2
3 NAD+
FADH2
3 NADH
FAD
+
3 H+
ATP
Figure 6.9A
ADP
+ P
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• The two carbons are added to a four-carbon
compound, forming citrate
– Which is then degraded back to the
starting compound
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8
• For each turn of the cycle
–
Two CO2 molecules are released
–
The energy yield is one ATP, three NADH,
and one FADH2
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citrate
+ H+
NADH
NAD
+
5
CO2 leaves cycle
2
CITRIC ACID CYCLE
NAD
+
+
Malate
NADH + H
ADP + P
FADH2
4
ATP
Alpha-ketoglutarate
FAD
3
CO2 leaves cycle
Succinate
NADH
+ H+
NAD
Step 1
Steps 2 and 3
Acetyl CoA stokes the furnace.
NADH, ATP, and CO2 are
generated during redox
reactions.
Figure 6.9B
+
Steps 4 and 5
Redox reactions generate
FADH2 and NADH.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6.10 Most ATP production occurs by oxidative
phosphorylation
• Electrons from NADH and FADH2
– Travel down the electron transport chain
to oxygen, which picks up H+ to form
water
• Energy released by the redox reactions
– Is used to pump H+ into the space
between the mitochondrial membranes
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• In chemiosmosis, the H+ diffuses back through the
inner membrane through ATP synthase complexes
–
Driving the synthesis of ATP
H+
.
H+
Inner
mitochondrial
membrane
FADH2
Electron
flow
NADH
H+
H+
Electron
carrier
Intermembrane
space
Mitochondrial
matrix
H+
H+
H+
Protein
complex
H+
H+
ATP
synthase
FAD
NAD+
H+
1 O
H+
2 2 +2
H+
H+
H2 O
Electron Transport Chain
ADP
+
P
H+
ATP
Chemiosmosis
OXIDATIVE PHOSPHORYLATION
Figure 6.10
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9
CONNECTION
6.11 Certain poisons interrupt critical events in cellular
respiration
• Various poisons
–
Block the movement of electrons
–
Block the flow of H+ through ATP synthase
–
Allow H+ to leak through the membrane
Cyanide,
carbon monoxide
Rotenone
+
H
+
H
+
Oligomycin
+
H
+
H
H
+
H
+
H
+
H
+
H
ATP
Synthase
DNP
FADH2
NADH
NAD
FAD
+2 H+
1 O2
2
+
+
H
+
H
ADP + P
H2 O
+
H
Electron Transport Chain
Figure 6.11
ATP
Chemiosmosis
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6.12 Review: Each molecule of glucose yields many
molecules of ATP
• Oxidative phosphorylation, using electron transport and
chemiosmosis
–
Produces up to 38 ATP molecules for each
glucose molecule that enters cellular respiration
Electron shuttle
across membrane
Cytoplasm
Mitochondrion
2 NADH
2 NADH
(or 2 FADH2 )
2 NADH
GLYCOLYSIS
2
Glucose
Pyruvate
2 Acetyl
CoA
+ 2 ATP
6 NADH
CITRIC ACID
CYCLE
+ 2 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
+ about 34 ATP
by oxidative phosphorylation
About
38 ATP
Figure 6.12
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6.13 Fermentation is an anaerobic alternative to
cellular respiration
• Under anaerobic conditions, many kinds of cells
– Can use glycolysis alone to produce
small amounts of ATP
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• In lactic acid fermentation
– NADH is oxidized to NAD+ as pyruvate is
reduced to lactate
2
2
NAD+
2
NADH
NADH
2
NAD+
GLYCOLYSIS
2 ADP + 2
P
2
ATP
2 Pyruvate
Glucose
2 Lactate
Figure 6.13A
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• In alcohol fermentation
– NADH is oxidized to NAD+ while
converting pyruvate to CO2 and ethanol
2
NAD+
2 NADH
2
NADH
NAD+
2
GLYCOLYSIS
2 ADP
+2 P
Glucose
2
2
ATP
CO2 released
2 !Ethanol
2 Pyruvate
Figure 6.13B
Figure 6.13C
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INTERCONNECTIONS BETWEEN MOLECULAR
BREAKDOWN AND SYNTHESIS
• 6.14 Cells use many kinds of organic
molecules as fuel for cellular respiration
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11
• Carbohydrates, fats, and proteins can all fuel
cellular respiration
–
When they are converted to molecules that
enter glycolysis or the citric acid cycle
Food, such as
peanuts
Carbohydrates
Fats
Sugars
Glycerol
Proteins
Fatty acids
Amino acids
Amino
groups
Glucose
G3P
Pyruvate
GLYCOLYSIS
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC
ACID
CYCLE
Acetyl
CoA
ATP
Figure 6.14
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6.15 Food molecules provide raw materials for
biosynthesis
• Cells use some food molecules and intermediates
from glycolysis and the citric acid cycle as raw
materials
• This process of biosynthesis
ATP needed to drive biosynthesis
ATP
–
Consumes ATP
CITRIC
ACID
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Proteins
Fatty
acids
Glycerol
Fats
Sugars
Carbohydrates
Cells, tissues, organisms
Figure 6.15
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6.16 The fuel for respiration ultimately comes from
photosynthesis
• All organisms
–
Can harvest energy from organic molecules
• Plants, but not animals
–
Can also make these molecules from inorganic
sources by the process of photosynthesis
Figure 6.16
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